This disclosure relates, in various embodiments, to electrostatographic imaging members. More specifically, the disclosure relates to an electrostatographic imaging member having a functionally improved outermost exposed imaging layer, such as a charge transport layer, which has an extended useful lifetime.
Electrostatographic imaging members are known in the art. Typical electrostatographic imaging members include (1) electrophotographic imaging members or photoreceptors for electrophotographic imaging systems and (2) electroreceptors such as ionographic imaging members for electrographic imaging systems. Generally, these imaging members comprise at least a supporting substrate and at least one imaging layer comprising a thermoplastic polymeric matrix material. In a photoreceptor, the photoconductive imaging layer may comprise only a single photoconductive layer or a plurality of layers such as a combination of a charge generating layer and one or more charge transport layer(s). In an electroreceptor, the imaging layer is a dielectric imaging layer.
Electrostatographic imaging members can have a number of distinctively different configurations. For example, they can comprise a flexible member, such as a flexible scroll or a belt containing a flexible substrate. The flexible imaging member belt may be prepared in a seamed or seamless configuration. The electrostatographic imaging member can also comprise a rigid member, such as those utilizing a rigid substrate drum. Drum imaging members have a rigid cylindrical supporting substrate bearing one or more imaging layers. Although the present disclosure is equally applicable to imaging members of any configuration, the disclosure herein after will focus primarily on flexible electrophotographic imaging members such as a flexible seamed belt.
Flexible electrophotographic imaging member seamed belts are typically fabricated from a sheet which is cut from a web. The sheets are generally rectangular in shape. The edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the more desirable method of joining because it is rapid, clean (no solvents) and produces a thin and narrow seam. In addition, ultrasonic welding is more desirable because it causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers therein to produce a strong fusion bonded seam.
A typical flexible electrophotographic imaging member belt comprises at least one photoconductive insulating layer. It is imaged by uniformly depositing an electrostatic charge on the imaging surface of the electrophotographic imaging member and then exposing the imaging member to a pattern of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the imaging member while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking toner particles on the imaging member surface. The resulting visible toner image can then be transferred to a suitable receiving member or substrate such as paper.
A number of current flexible electrophotographic imaging members are multilayered photoreceptors that, in a negative charging system, comprise a substrate support, an electrically conductive layer, an optional charge blocking layer, an optional adhesive layer, a charge generating layer (CGL), a charge transport layer (CTL), and an optional anti-curl back coating at the opposite side of the substrate support. In such an electrophotographic imaging member design, the CTL is the outermost layer and is exposed to the environment. Since flexible electrophotographic imaging members exhibit upward curling after the application of a CTL, an anti-curl back coating is usually employed on the back side of the flexible substrate support (the side opposite from the electrically active layers) to render the imaging member flat.
In a typical machine design, a flexible imaging member belt is mounted over and around a belt support module comprising numbers of belt support rollers, such that the top outermost CTL is exposed to all electrophotographic imaging subsystems interactions. Under normal operating conditions, the top exposed CTL surface of the flexible imaging member belt is constantly subjected to physicalmechanicalelectricalchemical species interactions such as the mechanical sliding actions of cleaning blade and cleaning brush, electrical charging devices, corona effluents exposure, developer components, image formation toner particles, hard carrier particles, receiving paper, and the like during dynamic belt cyclic motion. These interactions against the surface of the CTL have been found to cause surface scratching, abrasion, and rapid CTL surface wear; in some instances, the CTL wears away by as much as 10 micrometers after approximately 20,000 dynamic belt imaging cycles. Excessive CTL wear is a serious problem because it causes significant change in the charged field potential and adversely impacts copy printout quality. Another consequence of CTL wear is the decrease of CTL thickness alters the equilibrium of the balancing forces between the CTL and the anti-curl back coating and impacts imaging member belt flatness. The reduction of the CTL by wear causes the imaging member belt to curl downward at both edges. Edge curling in the belt is an important issue because it changes the distance between the belt surface and the charging device(s), causing non-uniform surface charging density which manifests itself as a “smile” print defect on paper copies. Such a print defect is characterized by lower intensity of print-images at the locations over both belt edges. The susceptibility of the CTL surface to scratches (caused by interaction against developer carrier beads and hard particulate from paper debris) has also been identified as a major imaging member functional failure since the scratches manifest themselves as print defects.
In a rigid electrophotographic imaging member drum design utilizing a contact AC Bias Charging Roller (BCR), ozone species attack on the CTL polymer binder is more pronounced because of the close vicinity of the BCR to the CTL of the imaging member drum.
Some current CTLs have a high surface energy of about 39 dynescm. The surface of the CTL is therefore prone to collect toner residues, dirt/debris particles, and additives from receiving papers. The eventual fusion of these collected species causes the formation of comets and filming over the outer surface of the CTL, further degrading the image quality of printouts. Another problem associated with high surface energy is that it also impedes the cleaning blade and cleaning brush function.
There is a need for imaging members which exhibit good abrasion/wear/filming resistances, surface lubricity, and durability. Such imaging members have enhanced physicalmechanical service life.